Rapid, well-controlled, and safe methods to limit bleeding in vessels have encouraged the development of endovascular devices and techniques, and their introduction into clinical practice. Early devices used balloons, either non-detachable or later detachable, in order to block vessels, for example, in the treatment of carotid-cavernous fistulas and saccular aneurysms.
Typically made from latex or silicone, balloons are delivered to a desired location in a vessel, then inflated in order to physically occlude the vessel. While other devices have since been developed, balloon occlusion remains in use, and is indicated for use in treating a variety of life-threatening conditions, including for example, giant cerebral and skull base aneurysms, traumatic and non-traumatic vessel injury or rupture, vertebro-vertebral arteriovenous fistulas, and pre-operative tumor resections.
Detachable balloons are also useful clinically in procedures outside of neurological intervention. For example, balloons can be useful in flow reduction procedures such as shunt occlusion in patients with transjugular intrahepatic portosystemic shunts and hepatic insufficiency, intrahepatic arterioportal fistulas, treatment of varicoceles, shunt occlusion in patients with a Blalock-Taussig shunt, obliteration of pulmonary arteriovenous fistulas, arteriovenous malformations or aortopulmonary anastomoses, coronary arteriovenous fistulas, or renal arteriovenous fistulas. Detachable balloons are also used in preoperative devascularization before surgical resection of organs such as the kidney.
Calibrated flow reduction is required during treatment of various medical conditions. For example, distal splenorenal shunt procedure (DSRS) (i.e., splenorenal shunt procedure or Warren shunt), is a surgical procedure in which the distal splenic vein attached to the left renal vein. This procedure can be used to treat portal hypertension, its main complication (esophageal varices), and other medical conditions, such as in pediatric patients with surgically created cardiac or pulmonary shunts (congenital heart disease).
Another related medical procedure is the transjugular intrahepatic portosystemic shunt or transjugular intrahepatic portosystemic stent shunting (commonly abbreviated as “TIPS” or “TIPSS”) is an artificial channel within the liver that establishes communication between the inflow portal vein and the outflow hepatic vein. It is used to treat portal hypertension (which is often due to liver cirrhosis). Portal hypertension is a hypertension (high blood pressure) involving the portal vein system, which is composed by the portal vein, and its branches and tributaries. Portal hypertension may frequently lead to life threatening upper gastrointestinal bleeding (esophageal varices) and the buildup of fluid within the abdomen (ascites).
Normal values for portal vein pressure are between five and ten mmHg. Anything over 10 mmHg is elevated, while hypertension is over 12 mmHg. In clinical practice, the pressure is not measured directly until the decision to place a TIPS has been made. Corrected sinusoidal pressure (that is the wedged hepatic vein pressure minus free hepatic vein pressure) has generally been accepted as the minimally invasive gold standard for assessing the severity of portal hypertension.
A TIPS procedure becomes necessary when portal hypertension causes the left gastric vein and the umbilical vein to dilate, which causes venous blood to flow in reverse. This leads to varices in the esophagus and stomach, which in turn can lead to bleeding.
A TIPS procedure decreases the effective vascular resistance of the liver. The result is a reduced pressure drop across the liver sinusoids and a decreased portal venous pressure. This, in turn, lessens the pressure on the blood vessels in the esophagus so that future bleeding is less likely to occur. The reduced pressure also makes less fluid develop, although this benefit may take weeks or months to occur.
In order to perform TIPS procedure, an interventional radiologist creates the shunt using an image-guided endovascular (via the blood vessels) approach, with the jugular vein as the usual percutaneous entry site. In a TIPS procedure, a needle is introduced (via the jugular vein) and a tract is passed from the hepatic vein into the portal vein. Thereafter, the tract is dilated with a balloon. After placement of the tract, portal pressure is reduced and the coronary and umbilical veins no longer fill.